Integrated Liquid Water (ILW) above Bern
Klemens Hocke, Oliver Stähli, Niklaus Kämpfer, and Christian Mätzler
Institute of Applied Physics and Oeschger Centre for Climate Change Research
University of Bern, Bern, Switzerland
Why
LAA
is Integrated Liquid Water (= cloud liquid water path) climate relevant?
Bern, 2003-2013
g/m2)
1) Just 0.03 mm of ILW (or 30
reduces the incoming
shortwave radiation of the Sun by about 50%
2) Outgoing longwave radiation of Earth is absorbed by clouds
http://www.jordi.belp.ch
 Earth’s energy balance depends on small cloud droplets
Pyranometer
(2.8μm - 300nm)
Why is it difficult to measure ILW?
• optical and infrared instruments cannot measure inside
the cloud
• a satellite radiometer cannot separate the cloud
microwave emission from the land surface emission
accurately
• a ground-based microwave radiometer monitors ILW in
time at one place
• a radar is not sensitive enough for small values of ILW
Ahrens, 2012
ILW ✓
no ILW
TROWARA, microwave radiometer of
Uni Bern with channels at 21, 22, 31 GHz
Limitation: TROWARA cannot provide ILW data in presence of rain droplets
(much larger than cloud droplets)
Monitoring of ILW with the tropospheric water radiometer (TROWARA) at Bern
Climatology of Humidity at Bern (2003-2013)
Intercomparison:
TROWARA and Satellite (CM/SAF)
• ILW is about 1‰ of IWV (Integrated Water Vapour)
• Lower panel: Anomalies of incoming short wave radiation
(black line, projected SWR) are anti-correlated to ILW (red)
• Seasonal cycle of ILW is enhanced after 2009
Conclusion
 TROWARA continuously monitors ILW above Bern
 Daily, seasonal, interannual variations of ILW are captured
(also ILW fluctuations with periods > 10 sec)
 TROWARA is an independent source on cloud liquid water
valuable for climate models and satellites